Alzheimers disease is associated not only with progressive memory loss but also with a decline in the ability to allocate attention. Deficits in attention can contribute to the cognitive impairments in memory, language, and visuospatial domains and also to the disruption of such routine daily activities as driving. The memory disorder of Alzheimer's disease has been extensively investigated. In contrast, alterations of attention have been relatively less well studied. We propose to characterize aspects of visual spatial attention in patients with a clinical diagnosis of Probable Alzeheimer's Disease (PRAD) from the vantage point of a distritubet neurocognitive network approach. Specifically designed paradigms that we have tested in patients with focal unilateral cerebrovascular lesions will be used to dissect the complex phenomena of directed attention into exploratory-motor, representational-sensory and motivational-limbic components. These experimental paradigms will be administered to patients with PRAD and their controls to detect dissociations among the behavioral components of spatial attention and the presence of hemispatial asymmetries. Performance on experimental tasks will be compared with scores on neuropsychological tests of language and visuospatial functions in order to determine whether hemispatial asymmetries in attention are correlated with performance on tasks that emphasize left or right cerebral specialization, respectively. Performance on experimenttal tasks will also be compared with a measure of functional independence in daily living activities. All subjects will be tested at two times separated by an interval of nine months to determine if deficits and patterns of dissociation persist over time. These studies provide an extension of our previous work on the neurobiology of directed attention and the cognitive deficits associated with PRAD. They are intended to yield guidelines for quantifying visual attentional deficits that can be of potential use in the staging of PRAD, in assessing responses to medication and in classifying subtypes of patients in whom visual spatial attention deficits are a prominent feature.